Chemical Structure of

hair

Submitted By :- Mukti Arora

Asst. Prof. in Cosmetology

ACKNOWLEDGING

THE HAIR SCIENCE-GOING SCIENTIFIC WITH HAIR

INTRODUCING HAIR

Hair is a protein filament thatgrows from follicles found in

the dermis, or skin.

It is a thread-like outer growth

on our body.

The Scientific study of hair iscalled “Trichology.”

COMPOSITION OF HAIR:

Hair is chiefly composed of a protein called “KERATIN”. The chemical

composition of hair varies with its color.

Proteins, raw elements, amino acids and bonds work together in forming hair fiber.

Amino acids, the building blocks of protein, are made up of COHNS elements, (Carbon, Oxygen, Hydrogen, Nitrogen and Sulfur).

The average hair is composed of:

Carbon: 50.65%

Hydrogen: 6.36%Nitrogen: 17.14%

Sulphur: 5%

Oxygen: 20.85%

FORMS OF HAIR:

Straight Hair

Wavy Hair

Extra Wavy Hair

Straigh

t HairWavy

Hair

Extra

Wavy Hair

CHARACTERISTICS OF HAIR:

In describing hair, we usually speak of its texture, elasticity, porosity,

and density:

1) Texture: The texture of hair may be coarse, medium, fine, or very fine.

This is usually determined by the diameter of the hairs.

2) Porosity: It refers to the ability of the hair to absorb moisture. Hair that is

very porous takes less time to treat than does less porous hair.

3) Elasticity: It refers to the ability of hair to stretch beyond its normal

length and then spring back.

4) Density: It refers to the amount of hair per square inch on the scalp. The hair are said to be thin, medium or thick depending upon how

much hair there is.

STRUCTURE OF HAIR:

DIVISION OF HAIR:

There are two main divisions of Hair-

1. Hair Root: It is that portion of the hair structure located beneath the

skin surface. This the portion of the hair enclosed within the follicle.

2. Hair Shaft: It is that portion of the hair structure extending above the

skin surface.

STRUCTURE ASSOCIATED WITH HAIR

ROOT:

Hair Follicle: It is a tiny tube-like structure in the skin which is like a test tube that holds the hair root. Every hair on your body has its own

follicle.

Papilla: It is found at the base of the follicle. It is well supplied with

the blood vessels and nerves. It is through the Papilla that

nourishment reaches the Hair Bulb. Papilla contributes to the growth and regeneration of Hair and it has the ability to produce hair cells.

As long as the Papilla functions, the hair will grow.

Hair Bulb: It lies just above the papilla and fits over it tightly and is

nourished by the papilla.

STRUCTURE ASSOCIATED WITH HAIR

FOLLICLE:

Arrector Pili Muscle: It is a small involuntary muscle

attached to the underside of Hair Follicle.

Fear or cold contracts it causing the hair to stand up

straight giving the skin the appearance of “gooseflesh”.

Sebaceous Gland: It consists of little sacular structures

situated in Dermis.

Their ducts are connected to hair secretion of oily substance

Sebum gives luster and pliability to the hair and keeps the

skin soft and supple.

LAYERS OF HAIR

SHAFT

CUTICLE, CORTEX AND MEDULLA:

HAIR GROWTH AND

REGENERATION:

STAGES OF GROWTH CYCLE:

Scalp hair growth follows a cycle which has three stages:

1. Anagen: It is the first stage known as Active stage because hair grows actively in this stage. In this phase, scalp continues to grow anywhere from 2-6 years.

2. Catagen: At the end of anagen stage, hair growth slows down, the follicle shrinks, the bulb thickens and slightly lifts from the papilla. This stage is also called Transitional stage.

3. Telogen: This is the last stage which is also called resting phase. In this stage, papilla goes for rest for about 3 months and this stage ends when a new hair forming from the papilla pushes the old hair up and out. In this stage old hair is replaced by new hair. That’s why this stage is also called Replacement stage.

HENCE THE CYCLE IS REPEATED AGAIN!

Hairstylists play an important role in many people’s

lives.

All hair services must be based on a thorough

understanding of the growth, structure, and

composition of hair.

Structures of the Hair Root

Hair follicle

Distribution

Growth

Hair bulb

Dermal papilla

Arrector pili muscle

Sebaceous glands

STRUCTURES OF THE HAIR ROOT

• Hair follicle: The hair follicle is the tube-like

depression or pocket in the skin or scalp that

contains the hair root. Hair follicles are

distributed all over the body, with the

exceptions of the palms of the hands and the

soles of the feet. The follicle extends

downward from the epidermis into the dermis

(the inner layer of skin), where it surrounds

the dermal papilla. Sometimes more than one

hair will grow from a single follicle.

• Hair bulb: The lowest area or part of a hair

strand, it is the thickened, club-shaped structure

that forms the lower part of the hair root. The

lower part of the bulb fits over and covers the

dermal papilla.

• Dermal papilla: A small, cone-shaped elevation

located at the base of the hair follicle that fits into

the hair bulb; it contains the blood and nerve

supply that provides the nutrients needed for

growth.

• Arrector pili muscle: These are minute,

involuntary muscle fibers in the skin inserted in

the base of the hair follicle. Fear or cold causes

them to contract, which makes the hair stand up

straight, resulting in goose bumps.

• Sebaceous glands: These are the oil glands of

the skin and are connected to the hair follicles.

The sebaceous glands secrete an oily

substance called sebum, which lubricates the

hair and skin.

Structures of the Hair Shaft

Hair cuticle

Cortex

Medulla

STRUCTURES OF THE HAIR SHAFT

• The hair cuticle is the outermost layer of the hair;

it consists of a single, overlapping layer of

transparent, scale-like cells that overlap like

shingles on a roof. The cuticle layer provides a

barrier that protects the inner structure of the hair

as it lies tightly against the cortex. It is responsible

for creating the shine and the smooth, silky feel of

healthy hair.

• The cortex is the middle layer of hair; it is a

fibrous protein core formed by elongated

cells containing melanin pigment. About 90

percent of hair weight comes from the

cortex. Protein structures located in the

cortex provide hair elasticity. Changes

resulting from chemical services occur in the

cortex.

• The medulla is the innermost layer. It is

composed of round cells. Very fine and

naturally blond hair may not even have a

medulla. Thick coarse hair and beard hair

always contain a medulla. The medulla is

not involved in salon services.

Learn About the Chemical Composition of Hair

Hair is approximately 90 percent protein.

The protein is made up of long chains of amino

acids, which, in turn, are made up of elements.

The major elements that make up human hair are

carbon, oxygen, hydrogen, nitrogen, and sulfur

and are often referred to as the COHNS elements.

These five elements are also found in skin and nails.

COHNS Elements

Carbon – 51 percent

Oxygen – 21 percent

Hydrogen – 6 percent

Nitrogen – 17 percent

Sulfur – 5 percent

Keratinization

Keratinization – ­­maturing process of living cells

that originate within the hair follicle.

As these newly formed cells mature, they fill up

with a fibrous protein called keratin.

KERATINIZATION

• Hair is composed of protein that grows from cells

originating within the hair follicle. This is where the

hair begins. As soon as these living cells form, they

begin their journey upward through the hair follicle.

They mature in a process called keratinization.

•As these newly formed cells mature,

they fill up with a fibrous protein called

keratin. After they have filled with

keratin, the cells move upward, lose

their nucleus, and die. By the time the

hair shaft emerges from the scalp, the

cells of the hair are completely

keratinized and are no longer living. The

hair shaft that emerges is a nonliving

fiber composed of keratinized protein.

Amino Acids

Linked like pop beads

Peptide or end bonds

Polypeptide chain

Helix

Side Bonds of the Cortex

Hydrogen bonds

Salt bonds

Disulfide bonds

Lanthionine bonds

SIDE BONDS OF THE CORTEX

• The cortex is made up of millions of

polypeptide chains.

• Polypeptide chains are cross-linked like the

rungs on a ladder by three different types of

side bonds that link the polypeptide chains

together and are responsible for the extreme

strength and elasticity of human hair.

• They are essential to services such as wet

setting, thermal styling, permanent waving,

and chemical hair relaxing.

• The three types of side bonds are hydrogen, salt,

and disulfide bonds.

• A hydrogen bond is a weak, physical, cross-link

side bond that is easily broken by water or heat.

They are weak individually, but because there are so

many, they account for about one-third of the hair’s

strength.

• A salt bond is another weak, cross-link side bond

that can be broken by changes in pH. They are

easily broken by strong alkaline or acidic solutions

and account for about one-third of the hair’s overall

strength.

• Disulfide bond: A strong, chemical side bond that

joins the sulfur atoms of two neighboring cysteine

amino acids to create cystine. The cystine joins

together two polypeptide strands. Although there are

far fewer disulfide bonds than hydrogen or salt bonds,

disulfide bonds are so much stronger that they also

account for about one-third of the hair’s overall

strength. Disulfide bonds are not broken by water.

They are broken by permanent waves and chemical

hair relaxers that alter the shape of hair.

• Lanthionine bonds: The bond that occurs from

hydroxide chemicals relaxing the hair and breaking

the disulfide bonds.